It's really more about what kind of things people were posting from that VPN IP in the months/years before you. The abuse detection system will say "the tshirt spammer is back, flag this account" just because you used the same VPN as them.

I've definitely created a new account recently over VPN, posted a single question in a linux forum and then found the account was shadow banned.

You can always contact the reddit team and if your account is suspended wrongly, it would definitely be reinstated.

Also important to note that if you didn't post a lot, many subs will auto-remove content from low karma users. So it's possible to have misidentified a global shadow ban with a few subreddit's low karma filter. One of my spammer adversaries regularly games FreeKarma4U and a specific star wars game subreddit until they figure out our low karma filter threshold then they go nuts with the spam.